Am I misunderstanding something?

[lovEU]

Thomas, do you know an illustration somewhere on the web explaining this quirk/phenomenon?
--
regards, eric

 

[Svein Skogen]

First of all, a crop factor does NOT change the focal length of your lenses. Crop factor does about the same as a pair of scissors to a paper printout, and this is how it changes the FOV of your picture.

Secondary, and as has been pointed out by several here, the VR18-200 isn't truly 200mm at close focusing distances. Nor is the VR105/2.8 micronikkor f/2.8 at close focusing distances. Both match their specs when focused at infinity.

Svein
--
Hi! I'm a .signature virus!
Copy me into your .signature to help me spread!

 

[Les Olson]

Yes: as others have said, focal length is focal length is focal length. DX lenses have the focal length it says on the side and the camera makes no difference to that.

When dealing with dSLRs the "crop factor" and "35mm equivalent" should not be applied to anything, with very few exceptions. You would need to think about crop factor if you were going to use your D3 with a 35mm f/2, but it is in service so you are using a D300 instead, and you can only take one lens and your shooting position will be fixed, and you need to work out what lens will be about the same as the 35mm on the D3 (answer, 24mm). Otherwise you just frame the image and press the shutter.

The idea that you get a "gain" in focal length range with DX (so that, eg, "DX is better for nature photography") is wrong: all DX does is crop the image in the camera instead of letting you do it on the computer.

And while we are at it, the idea that DX gives you greater depth of field is also wrong. If you put (eg) a 50mm lens on a DX camera and another identical lens on an FX camera, and put the cameras side by side the images will have the same depth of field. They won't be the same images, of course: the DX image will be missing the edges of the FX image. If you walk away from the subject until the DX image and the FX image are the same the DX image will have greater depth of field, but it is the greater distance to the subject that is responsible, not the sensor.
--

'Some of the money I spent on booze, women and fast cars, but the rest I squandered' - George Best

 

[Thomas Comerford]

Thomas, do you know an illustration somewhere on the web explaining
this quirk/phenomenon?
--
regards, eric

Yep, I linked to some images in this post:
http://forums.dpreview.com/forums/read.asp?forum=1030&message=28780873

--
http://www.pixelfixer.org

 

[cycle61]

I just took 2 pictures, one with my 35mm prime and one with my
18-200mm at 35mm. Both pics are the same size.

Don't know what made me think the crop factor only applied to non-DX
lenses, But I see they are all the same.

Thanks all, you learn something new every day.

--
D200 with 18-200 kit lens

I'm glad this seems to have settled out on the side of truth and reason. You definitely threw yourself a curveball there by using the 18-200 with it's bizarre internal mechanisms as a tool for focal length comparison. Glad you seem to have a handle on how it all works now.

--
Feel free to critique, I'm here to learn.
-Nick Davis
http://cycle61.blogspot.com

 

[lovEU]

Yep, I linked to some images in this post:
http://forums.dpreview.com/forums/read.asp?forum=1030&message=28780873

Thanks, I've seen your post - quite interesting. But I guess I didn't express right myself.

I'd like to see a figure/graph/chart where one can understand what's going on inside different lenses producing those effects.

--
regards, eric